Impacts of invasive Acacia and land use pressures on river water quality across a hydrographic demarcation

Sustainable water management at the regional scale is increasingly challenged by land use change, anthropogenic activities and invasive alien species. Acacia species represents a growing concern due to its potential effects on catchment processes and river water quality. To analyse these dynamics, two Structural Equation Modeling (SEM) approaches were applied: Partial Least Squares-Path Modeling (PLS-PM) and Generalized Structured Component Analysis (GSCA-SEM). These approaches were applied to 16 river basins within the Galicia-Costa Hydrographic Demarcation (NW Spain), covering the hydrological years 2015 to 2023. Latent variables (LV) were ‘Anthropogenic Pressure’, ‘Nature’, ‘Acacia’ and ‘Water Quality’. PLS-PM results indicated that these factors explain 68.2% of ‘Water Quality’, with a negative relationship between ‘Anthropogenic Pressure’ (β = -0.431) and ‘Water Quality’, while ‘Nature’ positively influenced it (β = 0.395). Additionally, ‘Acacia’ had a negative impact on ‘Nature’ (β = -0.138). On the other hand, GSCA-SEM yielded consistent patterns, yielding a Goodness-of-Fit Index (GFI) of 0.973 and a Standardized Root Mean Square Residual (SRMR) of 0.077. Notably, ‘Acacia’ showed a negative influence on ‘Water Quality’ (β = -0.385). By integrating pressures at the scale of a hydrographic demarcation, this study provides the first regional assessment of the effects of Acacia invasion on river water quality using SEM-based approaches. Results demonstrate suitability of PLS-PM for regional water quality assessments based on limited monitoring networks, while highlighting the potential of GSCA-SEM for future applications. Overall, the proposed framework offers a transferable tool to support river basin management, prioritise restoration measures and improve regional water quality planning.